Alveolar ducts are respiratory pathways with incomplete walls and alveoli at their most distal segment. Gas exchange occurs across the respiratory membrane.
Respiratory bronchioles are connected to individual alveoli and to multiple alveoli along regions called alveolar ducts
Alveolar ducts end at alveolar sacs, common chambers connected to multiple alveoli
Alveolar ducts are lined with simple squamous epithelium, some smooth muscle cells, and an extensive network of capillaries surrounds each alveolus
Capillaries of alveolar ducts are surrounded by a network of elastic fibers
